1. Field of the Invention
The present invention relates to a semiconductor laser, and more specifically relates to a laser beam emitting unit using a semiconductor laser as a light source.
2. Description of the Related Art
Various methods have been proposed for stabilizing the laser beam emitted by a laser diode (hereinafter referred to as "LD") for use as a laser beam light source. A typical method among the aforesaid methods superimposes a high-frequency pulse on a direct electric current (DC) as the driving current to drive a LD. Electromagnetic waves are generated in devices using the aforesaid method by the high-frequency pulse from the electric current flowing through a circuit or the like used to superimpose a high-frequency pulse on a direct electric current. When electromagnetic waves are generated, for example, when electromagnetic waves penetrate and produce noise in the control portion that controls the laser beam emitted by the laser beam source, the beam emitted by the LD cannot be accurately controlled, thereby causing impaired operation.
Therefore, conventional devices use a conductive case to shield the entire printed circuit board (PC board) containing the high-frequency pulse generating circuit and the entire portion wherein flows the electric current that contains the high-frequency pulse.
The high-frequency pulse generating circuit requires wiring to connect it to the external power source and control portion and the like. When an access hole is provided in the conductive casing for the wiring, said access hole must be blocked with a conductive material after the wiring is in place to prevent leakage of the high-frequency pulse from said wiring access hole, thereby greatly increasing the number of manufacturing process steps required.
Further, the previously mentioned conductive case must inevitably be large enough to cover the entire PC board containing the high-frequency pulse generating circuit and the entire portion wherein flows the electric current that contains the high-frequency pulse. Consequently, the device becomes larger in size, which produces the accompanying disadvantages of increased cost and increased space required for installation.